1. Field of the Invention
The present invention relates generally to dispersants, for use in agricultural applications, in particular the present invention relates to methods for the dispersion of insoluble material with copolymeric dispersants which dispersions are formed with improved dispersibility and show improved suspensibility. The present invention also relates to methods of producing dispersible formulations, the formulations per se and methods of treating substrates with dispersions produced from such formulations.
2. Description of the Related Art
The active principles in many agricultural applications are largely hydrophobic or water insoluble in character and are, by necessity, often administered as finely divided solids suspended in aqueous media. The majority of these active principles are manufactured and marketed in concentrated form, possibly with the addition of other insoluble inert fillers, which are then diluted prior to application. For example, the active principle is typically available in the form of a suspension concentrate (SC), wettable powder (WP) or water dispersible granule (WG). However, due to the generally hydrophobic nature of the active principle, the addition of a suitable dispersant is essential in order to achieve an homogenous dispersion with a minimum of mixing, such as may be achieved readily by hand or with minimal mechanical mixing. Furthermore, once an homogenous dispersion is achieved, the resulting suspension must remain stable for a time sufficient, at least, to allow application by usual means such as spraying. Any settling, agglomeration or flocculation of the finely divided solid may lead to inconsistent and ineffective application as well as blockage of the spraying equipment. It is therefore necessary to provide a dispersant which provides easy and homogenous dispersion and results in a suspension which maintains its stability during the application of the aqueous dispersion.
Effective dispersants for use in these applications ideally provide a suspension with acceptable dispersibility, suspensibility and lack of agglomeration. The Collaborative International Pesticides Analytical Council (CIPAC Handbook Volume 1) defines methods that can be used for determining acceptable suspensibility (MT 15.1) and degree of agglomeration (MT 59.3). For example, in suspension concentrates so-called SC formulations, this can be achieved by the addition of about 3–5 w/w % of a standard dispersant. Wettable powder (WP) and water dispersible granule (WG) formulations generally require the addition of standard dispersant in the order of 6–7 w/w % in order to achieve acceptable suspensibility and degree of agglomeration as determined by a wet sieve retention test. (MT 59.3).
Currently used dispersants for SC formulations include ethylene oxide/propylene oxide block copolymer surfactants based on an hydrophobic moiety plus ethyleneoxide. Also used are ether phosphate derivatives of non-ionic surfactants, especially of tristyrylphenol ethoxylates. Conventional anionic surfactants used include sulphonated derivatives of arylformaldehyde condensates, polyacrylates and lignosulfonates.
Dispersants for WP and WG formulations are usually limited by the requirement that the dispersant be solid at ambient temperatures, be non-gelling and not dissolve the active principle. For these reasons, conventional non-ionic surfactants are often unsuitable, and anionic dispersants are preferred. Known effective dispersants for WP and WG formulations include sulphonated alkylnaphthalene/formaldehyde condensate salts and lignosulfonate salts.
α-Olefin-polycarboxylate copolymers are well known as dispersants in a wide range of applications including pigment dispersion, emulsion polymerisation, cosmetics and pesticidal compositions. As far back as 1972 the sodium salt of a maleic anhydride and diisobutylene copolymer was given an “exemption from tolerance” for use in pesticide formulations by the United States Environmental Protection Authority following a petition from Rohm and Haas Co. FR 2545325 describes the use of ammonium and alkali metal salts of maleic anhydride-diisobutylene copolymer in pesticide granules. Similarly, EP 201417 describes the use of copolymers of maleic anhydride with surfactants selected from sulfates and phosphates of ethoxylated phenol derivatives in WP and WG formulations. JP 62036302 describes copolymers having a molecular weight range of from 5000–20000 for use with granular agrochemical compositions. Maleic anhydride and diisobutylene copolymer derivatives are described for use in conjunction with CaCO3 and Mg salts for SC formulations in JP 06 09,302. The use of sulfonated derivatives of copolymers of maleic anhydride in water dispersable granules is also described in JP 58-131903.
French Patent No. 2,397,444 describes stable and concentrated dispersions of active materials which may be prepared from non-dusting powders or granular materials. It is necessary to separate the active material in the presence of a salt of an acidic resin, such as, for example, a copolymer of maleic anhydride and an α-olefinic compound; add an organic solvent which forms, together with the aqueous medium, a two-phase system; treat such two-phase system by adding a carrier substance thereto; and then isolate the product by a reduction in the volume of the organic phase by the addition of water, the solvent gradually transferring into the added water.